Emergency lighting systems are required by national life safety codes (and various national and local government codes) in virtually every building and office where the general public may visit or congregate. As such, emergency lighting systems are well-known in the art.
An emergency lighting fixture usually includes one or more light sources or lamps, an AC (alternating current) failure detection circuit, a battery to provide power when the AC power has been interrupted, and a trickle charger to keep the battery fully charged. Other features may be found on a specific emergency light fixture, but the primary function of the emergency light is to illuminate a path of egress from a building upon loss of power from the primary electrical supply system.
Many emergency lighting systems, with their associated battery packs, are surface mounted against a wall or ceiling. The lamps are pre-adjusted or aimed in a position and location so that the beam of light illuminates a path of egress.
In operation, the emergency light fixture is connected to an AC power supply. The AC current supplies power to a battery charger to ensure that the battery is always charged to its optimum level. When the AC current to the emergency lighting fixture has been interrupted (and presumably interrupted to the room or building where the lighting fixture is located), the AC detection circuit senses the interruption and immediately forms an electrical connection between the battery and the lamps, thereby activating the lamps. The AC detection circuit may be as simple as a solenoid switch that is held open by the AC power, and when AC power is lost, the solenoid switch closes, thereby forming the connection between the battery and lamps.
Surface mounted emergency lights are normally considered unattractive and detract from contemporary design and architecture. Also, surface mounted emergency lights are more susceptible to tampering and mischief (e.g., kids breaking the lights for “fun”). Because of this, recent attempts have been made to conceal the luminaire into a wall or ceiling, allowing it to be substantially hidden from view (and protected) under normal conditions when power is available, yet to allow the light source to become exposed in a position to illuminate the path of egress upon loss of electrical power.
Examples of prior concealed emergency light fixtures are disclosed in U.S. Pat. Nos. 4,802,065 to Minter et al.; 5,025,349 to Gow; 5,682,131 to Gow; 5,851,061 to Hegarty; 6,097,279 to Gow; 6,164,788 to Gemmell et al.; and 6,371,621 to Le Bel. These prior systems include significant deficiencies in performance, reliability and cost, thereby limiting their use.
U.S. Pat. No. 4,802,065 (Minter et al.) discloses an emergency light fixture that can only be mounted in a ceiling as it requires the force of gravity on the panels to open. Many public buildings which require emergency lights have high ceilings where mounting in a wall is preferred. Accordingly, Minter may not be a feasible option since wall-mounting would prevent the force of gravity from assisting in the opening of the panels.
U.S. Pat. No. 5,025,349 (Gow) discloses an emergency lighting fixture that must be mounted in a ceiling to provide a useable light pattern. In addition, Gow teaches the use of a bi-directional motor which has a higher probability of mechanical jams upon the failure of a limit switch. Moreover, bi-directional motors require relatively more complex reversing circuitry, which adds to the cost of the emergency lighting system.
U.S. Pat. No. 5,682,131 (Gow) discloses a retractable annunciator that utilizes a bi-directional motor and its associated reversing circuitry to operate.
U.S. Pat. No. 5,851,061 (Hegarty) discloses a recessed emergency lighting fixture in which the light source remains inside the enclosure of the fixture and an external mirror controls the light beam. The light source/mirror arrangement requires additional ventilation. The additional ventilation requirement may increase the relative cost of the Hegarty fixture, and may make the fixture unfeasible for certain locations. Also, the position of the light source limits the ability to adjust the direction of the light beam.
U.S. Pat. No. 6,097,279 (Gow) discloses a retractable annunciator that requires a bi-directional motor and its associated reversing circuitry to operate.
U.S. Pat. No. 6,164,788 (Gemmell et al.) teaches a concealed, drop-down emergency light unit that operates under the force of gravity to open a pivotally-mounted door. Accordingly, a wall mount is generally not feasible for a Gemmell light unit. Further, the door does not rotate a full 180 degrees, thereby restricting the adjustment options of the lamps. Even further, Gemmell implements a drive system employing multiple gears and a clutch mechanism that increases the cost and complexity of the light unit.
U.S. Pat. No. 6,371,621 (Le Bel) discloses a servo-controlled emergency lighting fixture that uses a relatively complex hinge arrangement that must both pivot and translate the cover relative to the housing. Le Bel also teaches the use of a pulse proportional servo-motor. Pulse proportional servo-motors are undesirable due to their cost and their susceptibility to mechanical jams should a limit switch fail. In addition, Le Bel's drop-down cover requires gravity assistance making wall placement of the lighting fixture unfeasible.